Laminated ceramic electronic component

ABSTRACT

A laminated ceramic electronic component having excellent mechanical characteristics and internal electrode corrosion resistance, high degree of freedom in ceramic material design, low cost, and low defective rate includes a laminate having a plurality of laminated ceramic layers and a plurality of Al/Cu alloy-containing internal electrodes at specific interfaces between ceramic layers; where the Al/Cu ratio of the Al/Cu alloy is 80/20 or more.

This is a continuation of application Serial Number PCT/JP2011/052521, filed Feb. 7, 2011, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a laminated ceramic electronic component, such as that represented by a laminated ceramic capacitor, and more particularly relates to one including an internal electrode having an Al alloy as a component.

BACKGROUND ART

A laminated ceramic electronic component according to the present invention will be first described using the laminated ceramic capacitor 1 shown in FIG. 1 as an example.

The laminated ceramic capacitor 1 includes a laminate 2 having a plurality of internal electrodes 4 and 5 formed along specific interfaces between laminated dielectric ceramic layers 3.

First and second external electrodes 6 and 7 are formed at mutually different locations on the outer surface of the laminate 2. In the laminated ceramic capacitor 1 shown in FIG. 1, first and second external electrodes 6 and 7 are formed on mutually opposite end surfaces of the laminate 2. Internal electrodes 4 and 5 include a plurality of first internal electrodes 4 electrically connected to the first external electrode 6 and a plurality of second internal electrodes 5 electrically connected to the second external electrode 7, and the first and second internal electrodes 4 and 5 are arranged alternately with respect to the laminating direction.

For the internal electrode of the laminated ceramic electronic component, various metal elements are conceivable, but base metals are often considered for the purpose of cost reduction.

However, since base metals are very easily oxidized when co-fired with a ceramic, it has been necessary to have a reducing atmosphere as the atmosphere during firing and to precisely control the temperature condition and the oxygen partial pressure. As a result, material design has been considerably limited. In addition, there have been concerns of delamination resulting from an uneven stress associated with co-firing, and so on.

In the case of using an internal electrode made of a base material alone, there has been concerned about the corrosion resistance of the internal electrode if the ceramic laminate after being fired is exposed to a high-temperature and high-humidity environment.

For example, Patent Document 1 discloses a laminated ceramic electronic component using a base metal alloy as an internal electrode material. Specifically, the base metal alloy is a Ni/Al alloy and a Ti/Al alloy.

PRIOR ART PATENT DOCUMENT

-   Patent Document 1: JP 6-84608 A

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In the laminated ceramic electronic component in Patent Document 1, the firing atmosphere is a nitrogen atmosphere, and therefore a re-oxidation treatment of the ceramic material is required, so that the process is complicated.

Further, the laminated ceramic electronic component in Patent Document 1 has a problem in that a heavy stress is applied due to influences of shrinkage behaviors when reducing the temperature during a firing process, and thus delamination easily occurs.

Thus, an object of the present invention is to provide a laminated ceramic electronic component including an internal electrode made of a base metal alloy, wherein mechanical troubles such as delamination are inhibited, and firing can be performed even in the air.

Means for Solving the Problem

The present invention provides a laminated ceramic electronic component including: a laminate which has a plurality of laminated ceramic layers and a plurality of internal electrodes formed along specific interfaces between the ceramic layers and having an Al/Cu alloy as a component; and an external electrode formed on the outer surface of the laminate, wherein the Al/Cu ratio of the Al/Cu alloy is 80/20 or more.

Advantages of the Invention

According to the present invention, a laminated ceramic electronic component can be obtained in which occurrence of delamination is inhibited because stresses applied to ceramic layers from internal electrodes are low. In addition, a fixed amount of Cu is combined with the Al of the internal electrode to improve the corrosion resistance of the internal electrode, so that a laminated ceramic electronic component having high reliability even in a high-humidity environment can be obtained.

In addition, the laminated ceramic electronic component of the present invention is capable of being fired in the air even though the internal electrode is made of a base metal, and therefore the degree of freedom in ceramic material design is improved. Accordingly, a laminated ceramic electronic component having various properties can be obtained.

BRIEF EXPLANATION OF DRAWING

FIG. 1 is a view showing a laminated ceramic capacitor that is an example of a laminated ceramic electronic component of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A laminated ceramic electronic component of the present invention has internal electrodes having an Al/Cu alloy as a main component. If the Al/Cu ratio is 80/20 or more, the stress concentration between ceramic layers and internal electrodes is relieved, so that a delamination defect is effectively suppressed.

If the laminated ceramic electronic component of the present invention has an oxygen partial pressure of 1×10⁻⁴ MPa or more (including the pressure in the air), the surface part of the internal electrode, i.e. a site contacting the ceramic layer, may be constituted by a layer having Al₂O₃ as a main component. This results principally from oxidation of the surface of the Al internal electrode. This Al₂O₃ layer prevents electrode breakage of the Al internal electrode, and keeps the conductivity of the Al internal electrode satisfactory. This Al₂O₃ layer also has an effect of smoothing the Al internal electrode layer. For exhibiting these effects, the thickness of Al₂O₃ layer is preferably 0.25% or more of the thickness of the internal electrode.

If the thickness of the Al₂O₃ layer is more than 10% of the thickness of the internal electrode, Al₂O₃ constitutes 20% of the total thickness of the internal electrode layer, and the improvement of the conductivity is compromised. Accordingly, the thickness of Al₂O₃ layer is preferably 10% or less of the thickness of the internal electrode.

A method for producing the laminated ceramic electronic component of the present invention will now be described using a laminated ceramic capacitor as an example.

First, a ceramic raw material is prepared. The ceramic raw material is mixed with an organic binder component, as required in a solvent, and thereby formed into a ceramic slurry. By sheet-molding the ceramic slurry, a ceramic green sheet is obtained.

Next, an internal electrode having an Al/Cu alloy as its main component is formed on the ceramic green sheet. For achieving this, there are several methods, among which a method of screen-printing in a desired pattern a conductive paste containing an Al/Cu alloy powder and an organic vehicle is convenient. In addition, there are a method of transferring a metal foil and a method of forming an Al/Cu film while carrying out masking by a vacuum thin film formation method.

In this way, ceramic green sheets and internal electrode layers are stacked in multiple layers, and brought into close contact with one another under pressure to thereby a raw laminate before firing.

The raw laminate is fired in a kiln under a predetermined atmosphere and temperature. For example, if the oxygen partial pressure during firing is 1×10⁻⁴ MPa or more and the firing temperature is 600° C. or more, oxidation of the surface of the internal electrode may proceed to form an Al₂O₃ layer having a moderate thickness. If the firing temperature is 1,000° C. or less, electrode breakage of the internal electrode is easily effectively prevented. Concerning the oxygen partial pressure, atmospheric pressure is most preferable when considering convenience of the process.

If the rate of temperature rise from room temperature to the maximum temperature in the firing process is 100° C./minute or more, an Al₂O₃ layer is easily formed on the surface of the internal electrode more reliably even though various changes, such as a change in ceramic material composition, occur.

It is to be noted that Al has a melting point of about 660° C., but can be co-fired with a ceramic even at a temperature of 660° C. or more according to the production method of the present invention. This is ascribable to the Al₂O₃ layer formed on the surface part of the Al internal electrode. Thus, a high degree of freedom is also provided for material composition design of the ceramic used, and a variety of applications can be covered.

It is to be noted that the ceramic composition in the laminated ceramic electronic component of the present invention is not particularly limited. A variety of materials can be applied within the bounds of not impairing the object of the present invention, such as barium titanate-based compounds (including those substituted with Ca, Sr, Zr and the like), lead titanate-based or lead zirconate titanate-based compounds, alumina-based glass ceramics, ferrites and transition element oxide-based semiconductor ceramics.

The laminated ceramic electronic component of the present invention is applicable not only to a laminated ceramic capacitor, but also to a variety of electronic components such as a laminated piezoelectric element, a laminated thermistor element, a laminated chip coil and a ceramic multi-layered substrate.

Example

In this Example, the Al/Cu ratio in the internal electrode was changed, and the effect thereof on delamination were examined. Three ceramic materials having different compositions were prepared.

First, powders of BaTiO₃, Bi₂O₃ and CuO were prepared as a first ceramic material. These powders were mixed so as to satisfy the composition ratio described in “Material 1” in Table 1 to obtain a first ceramic raw material.

Similarly, powders of (Pb_(0.88)Bi_(0.12)) (Ti_(0.50)Zr_(0.50))O₃ and LiBiO₂ were prepared as a second ceramic material. These powders were mixed so as to satisfy the composition ratio described in “Material 2” in Table 1 to obtain a second ceramic raw material.

Similarly, powders of BaTiO₃, Bi₂O₃ and SiO₂ were prepared as a third ceramic material. These powders were mixed so as to satisfy the composition ratio described in “Material 3” in Table 1 to obtain a third ceramic raw material.

An ethanol-based organic solvent and a polyvinyl butyral-based binder were added to each of these ceramic raw materials, and the resulting mixture was mixed in a wet process by a ball mill to obtain a ceramic slurry. The ceramic slurry was sheet-molded to obtain a ceramic green sheet.

On the other hand, Al/Cu alloy powders with the Al/Cu ratio changed within a range of 99.9/0.1 to 75/25 as described in Table 1 was prepared. The alloy powders were mixed an acetate-based organic solvent and a cellulose-based binder to obtain an Al/Cu paste.

Next, an Al/Cu pastes with the different Al/Cu ratios within a range of 99.9/0.1 to 75/25 was coated on each of the three ceramic green sheets by screen printing to form an Al/Cu paste layer. Ceramic green sheets coated with the Al/Cu paste were laminated so as to be arranged alternately in terms of the side at which the Al/Cu paste layer was drawn, and brought into close contact with one another under pressure to obtain a raw laminate.

The raw laminate was heated in the air at 270° C. to remove a binder. Thereafter, the temperature was increased at a temperature elevation rate of 100° C./minute, and the laminate was fired in the air at the firing temperature shown in Table 2. An Ag paste containing a BaO—SiO₂—BaO-based glass frit was coated on both end surfaces of the obtained laminate, and baked in the air at 600° C. to form an external electrode to be connected to the internal electrode.

The laminated ceramic electronic component thus obtained had a length of 2.0 mm, a width of 1.0 mm, a thickness of 1.0 mm, a thickness per ceramic layer of 15 μm, a thickness per internal electrode layer of 5 μm, and 30 effective layers contributing to an electrostatic capacity. The area of one internal electrode portion confronted by the internal electrode per layer was 1.7×10⁻⁶ m².

The electrostatic capacity and the dielectric loss (tan δ) were measured for the obtained sample to find if it was practical as a laminated ceramic electronic component, and there was no problem in conductivity of the internal electrode. A thin Al₂O₃ oxide film was formed on the surface of the internal electrode made of an Al/Cu alloy, and the smoothness and the continuity of the internal electrode were satisfactory.

Next, for 30 samples of each fired laminate, the presence/absence of delamination was inspected by ultrasonic flaw detection. A sample where any delamination could be observed at all was considered as a defective, and the number of such samples was shown in Table 1.

TABLE 1 Firing Al/Cu temperature Number of Material Material composition (atom) [° C.] defectives 1 85BaTiO₃ + 12Bi₂O₃ + 3CuO (mol %) 99.9/0.1  730 0/30 99/1  730 0/30 98/2  730 0/30 96/4  730 0/30 94/6  730 0/30 92/8  730 0/30 90/10 730 0/30 88/12 730 0/30 85/15 730 0/30 80/20 730 0/30 78/22 730 3/30 75/25 730 12/30  2 90(Pb_(0.88)Bi_(0.12))(Ti_(0.50)Zr_(0.50))O₃ + 99.9/0.1  750 0/30 10LiBiO₂ (wt %) 99/1  750 0/30 98/2  750 0/30 96/4  750 0/30 94/6  750 0/30 92/8  750 0/30 90/10 750 0/30 88/12 750 0/30 85/15 750 0/30 80/20 750 0/30 78/22 750 7/30 75/25 750 20/30  3 50BaTio₃ + 15SiO₂ + 35Bi₂O₃ 99.9/0.1  700 0/30 (mol %) 99/1  700 0/30 98/2  700 0/30 96/4  700 0/30 94/6  700 0/30 92/8  700 0/30 90/10 700 0/30 88/12 700 0/30 85/15 700 0/30 80/20 700 0/30 78/22 700 4/30 75/25 700 15/30 

It can be seen from the results in Table 1 that the number of delamination defectives was 0 in samples where the Al/Cu ratio in the internal electrode satisfied 99.9/0.1 to 80/20 in the laminated ceramic capacitors using each of the three ceramic materials described above. On the other hand, a delamination defect occurred for samples having an Al/Cu ratio of less than 80/20.

INDUSTRIAL APPLICABILITY

A laminated ceramic electronic component of the present invention is applicable for a laminated ceramic capacitor, a laminated piezoelectric element, a laminated thermistor, a laminated chip coil, a ceramic multi-layered substrate and the like. 

The invention claimed is:
 1. A laminated ceramic electronic component comprising a plurality of laminated ceramic layers and internal electrodes at a plurality of specific interfaces between the ceramic layers, wherein the internal electrodes comprise an Al/Cu alloy in which the Al/Cu atomic ratio is 80/20 or more.
 2. The laminated ceramic electronic component according to claim 1, wherein at least one internal electrode has a layer of Al₂O₃ on its surface.
 3. The laminated ceramic electronic component according to claim 2, wherein the Al₂O₃ is 0.25% to 10% of the thickness of the internal electrode.
 4. The laminated ceramic electronic component according to claim 1, wherein the ceramic comprises a titanate, zirconate, glass ceramic, ferrite or transition element oxide ceramic.
 5. The laminated ceramic electronic component according to claim 4, further comprising at least one external electrode on an outer surface of the laminate.
 6. The laminated ceramic electronic component according to claim 3, further comprising at least one external electrode on an outer surface of the laminate.
 7. The laminated ceramic electronic component according to claim 2, further comprising at least one external electrode on an outer surface of the laminate.
 8. The laminated ceramic electronic component according to claim 1, further comprising at least one external electrode on an outer surface of the laminate.
 9. The laminated ceramic electronic component according to claim 1, wherein the ceramic layer comprises a barium titanate-based perovskite compound, and the laminated ceramic electronic component is a laminated ceramic capacitor.
 10. The laminated ceramic electronic component according to claim 9, wherein at least one internal electrode has a layer of Al₂O₃ on its surface.
 11. The laminated ceramic electronic component according to claim 10, wherein the Al₂O₃ is 0.25% to 10% of the thickness of the internal electrode.
 12. The laminated ceramic electronic component according to claim 1, wherein the ceramic layer comprises a lead zirconate titanate-based perovskite compound, and the laminated ceramic electronic component is a laminated piezoelectric element.
 13. The laminated ceramic electronic component according to claim 12, wherein at least one internal electrode has a layer of Al₂O₃ on its surface.
 14. The laminated ceramic electronic component according to claim 13, wherein the Al₂O₃ is 0.25% to 10% of the thickness of the internal electrode. 